1. Field of the Invention
The present invention is directed to performance modifiers for silicate based glass compositions, more particularly to metal silicides as performance modifiers for silicate based glass compositions, and even more particularly to metal silicides in silicate based glass compositions for the improvement of properties such as the absorption of infrared energy or the transmittance of color. The present invention is also directed to both a method of producing a glass composition and the finished glass composition resulting from the admixing, heating, and melting of a metal silicide in the batch glass composition.
2. Background of the Invention
Base glass compositions generally include one primary ion as a network former. A network former is the primary cation in the glass composition that bonds with oxygen to create an amorphous network. Other cations may also be present in the amorphous network. However, a primary cation is generally considered one which is present in an amount of about 25 weight percent or greater in the glass composition. Silicon is one cation which serves as a network former to provide silicate based glasses. The silicon is generally added to a batch glass composition as silica (SiO.sub.2).
Performance modifiers are often added to a base glass composition to impart specific color and energy absorbance properties in the finished glass. The absorption of energy at specific wavelengths is often desirable to enable various uses for the glass compositions. Additionally, certain colors are preferred for various glasses for aesthetic reasons.
There are limitations within specific glasses that must be balanced or optimized when attempting to achieve desired color and energy transmittance properties. For example, certain ingredients may improve the absorption of near infrared energy while imparting an undesirable color or reducing the light transmittance. Thus, the optimization of a specific color or energy transmittance property often negatively impacts other desirable transmittance properties.
The glass industry is continuously seeking ways to improve solar attenuation properties in glass and thereby to improve the efficiency, and expand the use, of the resulting glass articles. Infrared absorbing, or heat reducing, silicate glasses are recognized within the art. In general, infrared absorbing silicate glasses involve the addition of specific colorants that impact the color and energy transmittance properties of the glass.
One method generally recognized for manufacturing heat or infrared radiation absorbing silicate glass is through the incorporation therein of iron. The iron is generally present in the glass as both ferrous oxide (FeO) and ferric oxide (Fe.sub.2 O.sub.3). The balance between ferrous and ferric oxide has a direct and material effect on the color and transmittance properties of the glass. As the ferrous oxide content is increased (as a result of chemically reducing ferric oxide), the infrared absorption increases and the ultraviolet absorption decreases. The shift toward a higher concentration of FeO in relation to the Fe.sub.2 O.sub.3 causes a change in the color of the glass from a yellow-green to a blue-green, which reduces the visible transmittance of the glass.
Thus, it is desirable in the glass industry to provide additional performance modifiers that provide a high degree of selectivity between the visible region and the infrared region of the spectrum. Selectivity is generally referred to as the difference between the transmittance of visible light and the attenuation of infrared energy. Additionally, it is important to balance a high degree of selectivity in the finished glass composition with a desired color.